Looper control system and method of operating for rolling mills



May 9, 1967 c. c. PULLEN CONTROL SYSTEM ANI) METHOD LOOPER f OF OPERATING FOR ROLLING MILLS 18, 1964 3 Sheets-Sheet l Filed Dec.

3 Sheets-Sheet 2 INVENTOR Char/es C. Pa//en C. C. PULLEN LOOPEH CONTROL SYSTEM ANO METHOD OF OPERATING FOR ROLLING MILLS May 9, 1967 Filed Dec. 18, 1964 May 9, 1967 c, c. PULLEN LOOPER CONTROL SYSTEM AND METHOD OF OPERATING FOR ROLLING MILLS 5 Sheets-Sheet 3 Filed Dec. 18, 3.964

INVENTOR Q Char/es Cl Pa//en 32 www NSN Sw United States Patent O 3,318,125 LOOPER CONTRL SYSTEM AND METHOD F OPERATING FOR ROLLING MILLS Charles C. Pullen, Bethlehem, Pa., assgnor, by mesne assignments, to Bethlehem Steel Corporation, a corporation of Delaware Filed Dec. 18, 1964, Ser. No. 419,310 19 Claims. (Cl. 72-14) This invention relates to a looper control system for the control of tension in a rolling mill. More particularly this invention relates to an electrical control system employing static control elements for controlling the raising and lowering of the looper and the speed of the mill controlled by the looper, from the time the looper is raised until after it is lowered.

Loopers are ordinarily used between mill stands in a rolling mill train for taking up any slack in the strip between stands occasioned by the roll drive motor speed on one stand being out of adjustment with the roll drive motor speed on an adjacent stand with relation to the reduction being taken in the strip in the two mills. Modern practice has been to use the movements of the loopers as they take up slack in the strip to operate a speed control which increases or decreases the speed of the roll drive motor on an adjacent mill stand to remove the slack in the strip. Since the looper must be down when a strip is being threaded through the mill and up when the strip is entered in the mill in order to control the slack, control systems have been designed to detect when strip is entered in the mill stands on both sides of the looper and raise the looper only when strip is in both stands.

nUnder ordinary conditions such detection systems will work satisfactorily. However, when one strip is closely following another strip through a rolling mill train, it is possible for the following strip to be in the mill stand ahead of the looper while the preceding strip is still in the mill stand following the looper, in which event the control systern may mistakenly raise the looper into the empty interval between the strips under the impression that a strip is present. If this occurs, the following strip will run head first into a raised looper and the mill will often be cobbled. The usual way to avoid this possibility has been to run strips through the mill an appreciable distance apart or else manually control the raising of the looper, at best an ineiiicient practice.

It has also been customary to discontinue automatic speed control of a mill stand from the looper when the looper is down or partially down and adjust the speed of the mill stand to a preset speed calculated to be suitable for the entrance of a new strip into the mill. In mills in which the stand preceding the looper is the controlled stand, it has now been found desirable to control the raising and lowering of the looper according to whether a strip is entered in the stand preceding the controlled stand-that is, the stand second preceding the looper rather than the stand immediately preceding the looperand the stand following the controlled stand in order that the looper may retract before the rear of the strip reaches the controlled mill stand in order to prevent whipping of the tail end of the strip. Difliculty has been encountered in such systems, however, because the looper retracts too soon and therefore does not maintain full control of the mill speed and also because the controlled stand returns to a preset speed while the strip is in it, which speed may well be incorrect. If this speed is too fast, the rear portion of the strip may be cobbled, while if it is too slow, the rear section of the strip may be stretched or torn off. Also if automatic control of the speed of the controlled stand is resumed as a result of strip being entered in the appropriate stands, or when the looper is itself raised as a result of this, then difficulty may again arise if two closely following strips are detected by the strip detectors and interpreted as a continuous strip extending through the controlled stand and passing over the looper.

A further disadvantage of previous looper control systems has been that all the individual control systems for individual stands must either be placed in automatic operation at exactly the same moment, or else in a correct serial order, in order to prevent cobbling of the mill. If each looper controls the speed of the preceding mill stand, then the first looper must be placed on automatic before the second, and the second before the third, and so forth down the line. This is because if an individual looper detects excessive slack in the strip it will slow down the preceding stand which it controls in order to remove the slack. This in effect feeds the slack back to the next preceding mill stand and so on down the rolling mill train until the slack exits from the rst stand in the train. If the next preceding stand is not under automatic control in every case, however, it will not be able to remove the slack fed to it and this slack may build up precipitously until the mill cobbles. The same principle holds in reverse if the stand after the looper is the one whose speed is controlled by the looper as in this case slack is fed towards the last stand in the train by speeding up each mill stand rather than towards the first stand in the train by slowing down each stand.

It is an object of the present invention therefore to provide a novel interlocking logic circuit in a looper control system for a rolling mill which will prevent the raising of the looper after it has once been lowered until a strip detector associated with a mill stand preceding the looper indicates that strip is entered in that stand and a strip detector associated with the mill stand following the looper has detected a strip in this mill stand after a period in which no strip has been detected in the mill stand.

It is a further object of the present .invention to provide a novel interlocking logic circuit in a looper control system which will prevent the reinitiation of automatic looper speed control of a mill stand after automatic control has been interrupted and returned. to manual control, until a strip detector associated with the stand preceding the looper indicates that a strip is entered in that stand, a second strip detector associated with the stand following the looper indicates that a strip is entered in that stand and a second interlocking logic circuit indicates to said tirst interlocking logic circuit that a strip detector associated with the second preceding mill stand has detected a period during which no strip is entered in that mill before the strip detector associated with the following mill stand has detected a period during which no strip is entered in that mill stand.

It is a still further object of the present invention to provide a looper control system for a rolling mill stand in which the lowering of the looper is initiated by the loss of a signal from a strip detector associated with the mill stand second preceding the looper but which initiation is delayed by a timing device for a period sucient to allow the end of the strip to travel to a point substantially nearer the mill stand preceding the looper.

It is a still further object of the present invention to provide a looper control system for a rolling mill stand, in which the lowering of the looper is initiated by the loss of a signal from a strip detector associated with the mill stand second preceding the looper, in which automatic control of the speed of the `controlled mill stand is removed from the looper as soon as the looper begins to retract and held at the last speed at which it was controlled until a strip detector associated with the controlled mill stand sends a signal indicating that the strip has left the controlled stand, at which time the speed of the controlled mill stand is returned to a preset speed.

It is a still further object of the present invention to provide a looper control circuit employing static logic elements in which both the raising of the looper after it has once been lowered, and the reinitiation of automatic speed control by the looper once it has been discontinued, cannot be reinitiated until a strip detector associated with a mill stand following the looper indicates in serial order, rst'that strip has dropped out of the mill stand, and second that strip has reenter/ed the roll stand and in which the reinitiation of automatic speed control by the looper is delayed by a timing element until the looper has been raised.

It is a still further object of the present invention to provide a looper control system in a rolling mill train in which a series of substantially separate static logic circuits are interlocked so that automatic speed control by loopers associated through the separate control systems with respective mill stands can be initiated only i-f al1 the control systems which are operationally previous to the control system in question have already been placed on automatic control.

It is a still further object of the lpresent invention to provide a method of operating a looper control system in which as a strip passes through a mill stand the speed of the mill stand is controlled by the movement of the looper until the rear end of the strip is a predetermined distance from the controlled mill stand, the looper is retracted when the end of the strip reaches a predetermined point, the speed of the mill stand is held at the last controlled speed until the strip leaves the controlled mill stand, and the speed of the mill stand is then automatically switched to a preset speed in preparati-on for the next strip, and preventing reraising of the looper and reinitiation of automatic speed control for the next strip until the rst strip has left the mill stand following the looper and the next strip has entered this stand.

The looper control system of the present invention consists of the following principle parts for each controlled mill stand: a bridge circuit to detect the deviation of the looper arm from a set point and initiate an appropriate error signal, a controller to modify this signal by ampli-cation and feedback to render the signal appropriate for its control function, a motor speed regulator modified by the control signal, a manual control circuit to control the speed of the mill stand when automatic control by the looper speed control is not present, and a static element logic and timing control circuit which operates appropriate switches associated iwith the controller to operate the controller, switch from manual control to automatic control and back again in response to signals from strip detectors associated with the mill stands following, preceding and second preceding the looper, and also operate control means to raise the looper. In addition each individual looper control systern is interlocked through its static logic circuits with preceding and/or following similar logic circuits to provide a definite sequence with regard to adjoining looper control circuits for the activation of the automatic speed control circuits of the individual looper control systems.

In the drawings:

FIGURE 1 diagrammatically shows a rolling mill train having an automatic gauge control and the looper control system of the present invention.

FIIGURE 2 shows the speed control circuits for the looper control system of FIGURE 1.

FIGURE 3 shows the logic control circuit which controls the switches in the speed control circuit of FIGURE 2 and operates valves to raise the loopers.

In FIGURE l are shown six rolling mill stands numbered from 5 to 10 which may constitute the finishing stands 1 to 4, not shown will be understood to be lo1 cated before the six finishing stands. Each mill stand is supplied With a screw control mechanism, sho'wn diagrammatically, land a screw setting, `also shown diagrammatically, by which the distance between the rolls is adjusted to control the gauge of strip coming out of the mill.

Mill stand 9 in addition has an automatic gauge control of any suitable type, which may be a so-called gagemeter system in which the roll position is automatically adjusted by running the screw position down to a reference point and then correcting for mill spring by means of an automatic calculation based on the load felt by a load cell. A similar automatic gauge control may be applied to each one of the mills if desired, but only one automatic gauge control has been shown in order to illustrate the use of a pivot stand as described hereinafter. An X-ray gauge is shown after stand to provide a check of the actual gauge of the strip issuing from the mill and provide an error signal to the gauge controller to remove any errors.

A load cell is provided for each mill to detect pressure between the rolls. In stand 9 the load cell detection signal is used to correct for the mill spring in the well known gagemeter system manner and in addition is used to detect the presence of a strip in the mill for the looper control system as will hereinafter be more fully described. Each of the other mill stands has a load cell associated with it, the signals of which are used to indicate to the looper control systems the presence or absence of a strip in each respective mill.

Between each mill stand is diagrammatically shown a looper. No. 1 looper is located between mill stands 5 and 6, looper No. 2 between mill stands 6 and 7 and so forth. Each looper may be raised and lowered by a conventional pneumatic cylinder arrangement, not shown, as is well known in the looper art. The valves controlling the admission of air to the air cylinder arrangement are controlled by solenoi-ds operated by the static element logic circuit hereinafter described. The loopers ordinarily have a movement range of six to eighteen inches and this movement operates a rheostat slide to vary an electrical signal to the speed matching controller as will be described hereinafter. As shown in FIGURE 1, the speed matching controller controls a speed regulator which in turn determines, together with the speed setting, the speed of the mill motor, not shown, which drives the rolls in the mill stands. The speed setting may be set manually or may be derived from a punched card or other automatic system. The speed matching controller controls the speed in a range determined by the basic speed set by the speed setting.

Mill stand 9 with its gauge control system is the pivot stand of the mill train. The speed of the rolls of this stand is preset and is not controlled by a looper. The basic speed of stands 5, 6, 7 and 8 is preset by the speed setting in each case but is varied during automatic speed control in each case by the looper following the mill stand, loopers 1, 2, 3 and 4 respectively. The speed of stand 10 is controlled within a set range by the movement of looper 5E preceding stand 10. A strip A is shown passing through the mill train `of FIGURE 1 in stands 8, 9 and 10 and a strip B is shown closely following in stands 5, 6 and 7 the tail end of strip A. Dotted lines C and D indicate positions at which, when the tail end of a strip passes, certain looper control actions will 'be initiated as hereinafter described.

The operation of the looper control system of the present invention will be particularly described with reference to the interaction of mill stands 6, 7 and 8, load cells 6A, 7A, and SA, looper 3, speed matching controller 29, and speed regulator 94.

In FIGURE 2 is shown the speed control circuit sys` tem for an individual looper by which the speed of the: mill motor may be controlled. The particular circuit shown in FIGURE 2 is the control circuit by which looper 3 in FIGURE l controls the mill motor of stand 7 to regulate slack `between mill stands 7 and 8. In a looper circuit boX, shown in broken outline at 11, is a looper contact arm 13 which is part of a bridge circuit 15 including the resistance 17 which arm 13 contacts, and resistance 19 which arm 21 contacts, Contact arms 13 and 21 are connected together through resistors 23 and 25. Resistances 17 and 19 are connected in parallel across a low voltage direct current source 27, located in a speed matching controller, shown in dotted outline at 29, through diode 39, terminals A7 and A8, and switch L31 in series with resistor 33. Capacitors 35 and 37 serve to ldamp out any transient alternating current oscillations which may tend to occur in D.C. power supply 27. Line 41 connects tap 43, between resistors 23 and 25, through terminal A4 and variable resistor 45 with switch K21, normally closed during automatic operation, to apply a control potential from the bridge circuit 15 through a second resistor 49 to one contact 53 of a synchronous converter 51. Common 55 connects bridge circuit 15 from tap 57 with ground 59 through terminal A6, and generally through terminal A5 with a second conl tact 61 of synchronous converter 51-via resistor 63,

variable resistor 65, normally closed switch K22, and resistor 69-and also with the feedback of the motor control circuits. Switches K21 and K22 are designed to be closed during automatic operation, which normally will be the most frequent mode of operation, and open during manual operation, Switch K11, indicated in the drawing as normally open, which connects common 55 through tap 69 with contact 53 of synchronous converter 51 through resistor 49, is closed only during manual operation when switch K21 is open to isolate the bridge circuit 15 from synchronous converter 51 as will be more clearly decsribed hereinafter. The operating coils for relays K1 and K2 are connected in parallel through terminals A1 and A2 with a switch L71 and diode rectifier 73 to a source of alternating current 75. -Relay K2, when operated, either opens or closes each switch, depending upon whether or not the switch is normally open or closed during automatic operation, similarly designated in FIGURE 2, for instance K21 and K22, while relay K1 in a similar manner appropriately opens or closes switches similarly designated, such as K11. Relay K2 is designed to operate a fraction of a second before relay K1 so that the K2 switches are all operated a fraction of a second before all the K1 switches. This may be accomplished by placing a small resistance 77 in series with K1 and a capacitor 78 in parallel with K2.

The potential which is tapped off synchronous converter contacts 153 and 61 by vibrating contact 79 is applied through capacitor 81 to the grid circuit of a vacuum tube or other similar element, not shown, in a suitable high gain amplifier 83 where the resulting alternating potential is considerably increased and then passed into a suitable demodulator 85 where the potential is converted to a direct current signal which passes through terminal B1, resistor 87 and meters 89 and 91 into the speed matching controller amplifier, indicated diagrammatically by a dotted outline 93, where it is applied t-o a winding 95 of a magnetic amplifier shown in dotted outline 97. After passing through magnetic amplifier 97, the direct current signal passes through common 55 to terminal B8 where it is shunted through load resistor 99 to terminal B5, to tap 101, through closed switch K12, and then through terminals B4 and B2 back to the positive terminal of demodulator 85.

A coil 92 in magnetic amplifier 97 is connected to speed regulator 94 which may comprise a magnetic amplifier, rectifier, and eld exciter, not shown, which apply direct current to motor field 100 to regulate the speed of armature 102 of mill motor 104 shown in dotted outline. Alternating current power source 98 supplies power t-o speed regulator 94 through double switch R96. Manual speed 6 adjustment 106 may be used to vary the speed of the mill motor 104.

A portion of the current reaching terminal B8 will divide at terminal B8 and, instead of passing through load resistor 99, will follow common 55 to tap 103 and from tap 103 flow through potentiometer 105 :and resistor 107 back to tap 101. A potential is tapped ofi potentiometer 105 and applied to contact 61 of synchronous converter 51 through capacitor 109, normally closed switch K23, and resistor 69.

A so-called reset system insures that in the long run the potential on contact 53 will be zero with respect to common 55. Capacitor 109, resistor 63, and variable resistor 65 supply the feedback voltage to Contact 61 to balance out changes in the voltage on Contact 53. When a potential change between tap 103 and the take-off from potentiometer 105 first occurs, capacitor 109 will transfer the potential difference from potentiometer 105 to contact 61. The potential occurring at tap 103, however, will also be transferred, via tap 111, through resistor 63, variable resistor 65, switch K22 and switch K23 to the opposite side of capacitor 109 to oppose the charge on capacitor 109. The rate at which the charge on capacitor 109 is altered is determined by the setting of variable resistor 65. The potential at tap 103 is thus slowly transferred to contact 61 of synchronous converter 51 until the potential on contact 61 originally derived from the load circuit through capacitor 109 disappears, or becomes zero with respect to common 55. Therefore a potential rapplied to contact 53 will cause the output current of demodulator 85 to continue to be reset until the potential on Contact 53 is ultimately restored to zero with respect to common 55.

In order to increase the corrective action of the final control circuit a rate action system is also provided. A potential is taken from tap 113 of the .bridge circuit :and applied through terminal A3 to capacitor 115 across which it is immediately transferred to contact '53 of synchronous converter 51 through resistor 49. The charge on capacitor 115 is progressively neutralized by potential leak-ing through variable resistor 45 from the bridge circuit to contact 53. The greater an error signal is received from the bridge circuit, and, in particular, the more suddenly it is applied, the greater potential will be placed across capacitor 115 to add algebraically to the potential more normally placed on contact 53 lthrough variable resistor 45, switch K21 and resistor 49.

The circuits described above are sufiicient to successfully operate the control system on automatic speed control. Manual control of the speed is, however, lalso connected through the controller in order that the controller may follow the speed of the mill motor in order to prevent large sudden changes in mill motor speed when switching from manual to automatic control.

Power to magneti-c amplifier winding 95 of magnetic amplifier 97 during manual operation may be suitably provided by a 30 volt D.C. power source 117 associated with a potentiometer 119 which taps off any desired voltage or current via terminal B6 to a circuit which includes switch K13, closed during manual operation; tap 101, terminal B5, since switch K12 will be open during manual operation, resistor 99, terminal B8, common 55, magnetic amplifier Winding 95 of the speed matching controller amplifier 93, meters 91 and 89, rand resistor 87.

During manual control of the speed regulator 94, demodulator 85 continues t-o provide 1a control signal but this signal is shunted, via tap 121, through a dummy load 123, which may comprise a suitable rheostat, tap 125, and a resistor 127, by switch K14, which is closed during manual operation; normally closed automatic operation switch K12 being opened during manual operation. Tap is also connected to common 55 through resistors 129 land 131 and tap 133. During manual operation a potential will be taken at a tap 135, between resistors 129 and 131, and applied through terminal B7 int-o the controller,

through switch K24 to tap 137, where, since normally closed switches K22 and K23 are open during manual operation, it is applied to contact 61 of synchron-ous converter 51. At the same time during manual operation, the potential occurring at tap 133 will be applied through common 55, tap 69, normally open but now closed switch K11, and resistor 49 to contact 53 of synchronous converter 51. During manual operation a line 145 connects capacitor 109 via tap 147, switch K25, tap 149 and tap 151 with the bridge circuit 15, and rate capacitor 115. This maintains a charge in the capacitor 109 during manual operation to prevent a large change in the output current of demodulator 85 when automatic control is reinitiated.

In magnetic amplifier 97 of speed matching controller amplifier 93 is an alternating current driving coil 139 in circuit with an alternating current source 143 through double switch L141.

In FIGURE 3 is shown the static logic circuit which sequences the `appropriate opening and closing of the various switches shown in FIGURE 2 plus the valves which control the raising and lowering of the looper.

In FIGURE 3 two alternating current power supplies 201 and 203 are shown connected by double switch R205 to a standard 120` volt 60 cycle source. A low voltage line connects contact 207 of power supply 201 and contact 209 of power supply 203. A line 211 passes to a control pulpit shown in dotted outline at 213 where the voltage in the line is applied in parallel across a switch R215, which manually activates automatic looper speed control operation, and a switch R217, which activates a manually controlled raising of the looper. Switch R215 operates relay 219,A which in turn operates switch L221 in the static logic circuit of FIGURE 3. Switch R217 activates relay 223, which in turn operates switch L225 in the static logic circuit. The circuit is completed by line 227 which returns to Contact 229 of power supply 203.

Switch L221 in the static logic circuit activates automatic control of the looper system. When switch L221 is closed, a signal is applied from common 231 to NOR logic element 235. Since it is the characteristic of NOR eleiments not to give out an energization signal unless a zero signal is applied to all their inputs, NOR element 235 gives out no si,gnal,vand a zero input, or, in other words, no signal, is applied to input A of NOR element 237.

If a signal is being supplied to NOR element 241 by the adjacent static logic circuit for looper 2, which sequences the operation of the preceding looper, indicating that this static logic circuit is also on automatic, then NOR element 241 will also provide a Zero signal and input B of NOR 237 will be zero. Since both inputs A and B of NOR 237 `are 'now zero NOR 237 provides an energizing signal which is applied via tap 243 to the input of NOR 245 and input B of NOR 247. The signal output of NOR 237 is also applied via tap 243 to terminal 249 which leads to the succeeding static logic circuit, not shown, which sequences the operation of the succeeding looper 4. Since NOR 245 is receiving an input, it puts out no signal and a zero input is consequently applied to input A of NOR 25-1.

Input B of NOR 251 will also receive a zero input if NOR 253 gives out a zero signal, which will occur only if a signal is received either by way of terminal 255 connected with load cell 8A of mill stand 8 to provide an energizing signal impulse at input A of NOR 253, or an impulse is received at input B of NOR 253 if manual operation switch L225 is closed to provide ya signal to initiate manually initiated manual operation. (There is also an automatically initiated manual setpoint speed control operation which is normally activated at the end of each strip by the automatic control system.)

When both the A and B inputs of NOR 251 are zero, NOR 2511 will put out an energization signal which is 8 applied through OR element 259, used merely as a signal collector or combiner, to input B of a suitable timing element 261 which will delay the signal a predetermined period vbefore allowing it to pass to NOR 263 which, when it receives a signal, puts out a zero signal.

Terminal `265 on power supply 201 is designed to provide a single brief pulse whenever power supply 201 is activated. This pulse is used to return all elements which should start out in a particular initial state to such initial state, and in the case of timer element 261, the brief pulse given out by terminal 25 is applied to input A of timer 251 through line 267 to reset the timer after a power failure or other interruption.

The zero signal given out .by NOR 263 as a result of receiving a signal from timer 261 is applied to input C of NOR element 269 of static logic element memory circuit 271. Input B of NOR 269 receives the brief pulse put out by terminal 265 of power supply 201 through line 267 if the power cornes on after a power failure. This pulse serves to reset the memory circuit 271 so that its action may always remain in the correct sequence. Unless the main power is off for a period, input B of NOR 269 will always be zero and will thus be in a go condition. Input A of NOR 269 receives a feedback pulse from the output of NOR element 273, the second NOR element of memory circuit 271. The output of NOR 269 is applied to feedback input A of NOR 273. Input B of NOR 273 receives a signal pulse from NOR 275. Input B or" NOR 275 will receive a signal if manual switch L225 is closed to place the control system on manual speed control. Input A of NOR 275 receives a signal from the output of NOR element 277, the input A of which receives a signal from NOR element 279, which in` turn receives a signal from terminal 281 connected to load cell 6A on mill stand #6, diagrammatically shown in FIGURE l. If NOR 279 receives a signal from load cell 6A the output of NOR 279 will ybe zero and the input A of NOR 277 will, consequently, also be Zero. Providing that input B of NOR 277 is also zero, an output signal will be sent from` NOR 277 to input A of NOR 275, and NOR 275` will apply a zero signal to NOR 273 of memory circuit 2711. Input B of NOR 277 receives a zero signal from NOR 245 when automatic control switch L221 is closed and all previous control systems are also on automatic.

The output of NOR 237 is applied to input B of NOR 247. The output of NOR 247 is applied to input C of NOR element 283 and the output of NOR 283 is applied through tap 285 to amplier 287, the output of which is in turn applied to the coils or" a solenoid 289 the armature of which is operatively connected to a suitable air valve, not shown, which controls the air to conventional pneumatic cylinders for raising the looper against the strip passing through the mill.

The signal from NOR 283 is also applied through tap 285 to timing element 291 which is designed to delay a signal impulse applied to it for a predetermined period before allowing it to pass through to input B of NOR element 293, which applies a zero signal from its output to .amplifier 295 designed to amplify any, signal applied to it and apply the amplied signal to the coils of solenoid 297, the armature of which operates a booster valve, not shown, in the pneumatic system which operates the air cylinders to raise the looper. The `booster valve is designed to be opened for a short period at the initiation of raising of the looper in order to move the looper more quickly at the beginning of its raise cycle. If the main power should fail, timer 291 would be reset by a brief pulse from line 267 when power is restored.

A signal from NOR 283 iwill also be applied via tap 285 to the input of NOR element 299, the output of which is applied to input A of NOR 293. It will be clear from an examination of the circuit that when NOR 283 gives out an energization signal, NOR 299 will provide a zero signal to input A of NOR 293, and, since the signal from NOR 283 is delayed an appreciable time by timer 291, a zero signal will also be applied to input B of NOR 293. Since both inputs of NOR 293 are zero, NOR 293 will give out an energizing signal which will be amplied by amplifier 295 and applied to solenoid 297. When, however, after a predetermined period, timer 291 tinally allows the signal from NOR 283 to pass, a signal will be applied to input B of NOR 293 and the output of NOR 293 will change to zero so that solenoid 297 no longer receives any current and the looper booster valve is closed.

Input B of NOR 283 will receive a zero input from NOR 253 when a signal is received at input A of NOR 253 from terminal 255 connected to load cell 8A on number 3 mill stand, or at input B from manual control switch L225. fInput A of NOR 283 will receive a zero input so long as the input of NOR element 301 is energized by the output of NOR 273 of memory circuit 271, or the input of NOR 301 is subjected to a zero input but the resulting output signal from NOR 301 has been delayed by timing element 303.

When an energizing signal is passed by timer 303 it is not only applied to input A of NOR 283 but also to the input of NOR element 305 which, in consequence, gives out a zero signal to input A of NOR element 307. If input -B of NOR 307 is also receiving a zero signal from the output of NOR 263, NOR 307 will provide an energization signal to input A of NOR element 309. If either NOR 263 or NOR 305 are providing an energizing signal, the output of NOR 307 will be zero and input A of NOR 309 will consequently also be zero. VIf either manual switch L225 or automatic switch L221 are closed, a zero output will be given out by NOR 247 and applied via taps 311 and 313 to the B input of NOR 309. If main switch R315 is closed, input C of NOR 309 will also receive a zero input from the output of NOR element 317 which receives its input through switch R315 from common 231. When inputs A, B and C of NOR 309 are all zero, NOR 309 will provide an energizing pulse at its output which is applied to amplifier 318, which in turn provides an amplified energization signal to solenoid 320 which, energized, opens hold switch L31 shown in FIGURE 2.

If main switch R315 is closed to provide an energizing signal to NOR 317, resulting in a zero -output signal from NOR 317 being applied to input A of NOR element 319, and a zero signal is also received at input B of NOR 319 from NOR 245 as a result of the looper logic circuit automatic switch L221 being closed and previous looper logic circuits for loopers 1 and 2 being set for automatic control, an energizing signal will be provided by NOR 319 to amplifier 321 which amplilies the signal and applies it to solenoid 323 which operates switch L141, shown in FIGURE 2, to energize amplifier driving coils 139 of the controller amplifier 93.

Terminal 325, which is connected to load cell 7A of mill stand 7, shown diagrammatically in FIGURE l, supplies any signal from the load cell to the input of NOR element 327. The output of NOR 327 is applied to input A of OR element 329 which will pass on any energization input to input A of a NOR element 331. Input B of NOR 331 arises from a signal from main switch R315 through the intermediary of NOR 317. Input C of NOR 331 is provided by the output of NOR 247 which will provide a zero signal output if either the manual switch L225 or the automatic operation switch L221 is closed. -Input A of NOR 331 is, therefore, the controlling input.

Input B of OR 329 will be L225 is open and not providing an energization signal. This cancels the effect of a zero signal received at input C of NOR 331 if switch L225 is closed, and input C of NOR 331, therefore,to all intents and purposes, provides a zero signal only if automatic operation switch zero only if manual switch 10 L221 is closed, resulting in a zero signal output from NOR 247. Input C of OR 329 is derived from the output of NOR 263 and is the same Ias input B of NOR 307 and input C of NOR 269 of memory circuit 271.

The output of NOR 331 is applied to the input 0f a NOR element 333 which provides an opposite output to input B of a NOR element 335 in a memory circuit 337. 'Input A of NOR 335 receives a signal from the output of a second NOR element 339 in memory circuit 337. Input C of NOR 339 receives as a signal the output of NOR 273 of memory circuit 271. Input B of NOR 339 receives a reset pulse when current is established in power source 201 after a power stoppage of any kind. Input A of NOR 339 of memory circuit 337 is a feedback signal received from NOR 335 of memory circuit 337. The output signal of NOR 335 of memory circuit 337 is also applied to amplifier 341 where an energization signal is amplified for the energization of solenoid 343 which operates switch L71, shown in FIG- URE 2, to operate relays K1 and K2, also shown in FIG- URE 2.

The operation of the looper control system will now be explained with respect to FIGURES 1, 2 and 3. In the drawings all swit-ches are shown in the positions in which they would be for automatic operation and the description will be made with respect to a typical sequence of automatic operation of the looper control system. The description, moreover, with respect to the specific control system elements, will be explained with respect to the control circuits which control the movements of looper 3, shown diagrammatically in FIGURE 1 and the speed of the motor or mot-ors which drive the rolls of mill stand 7, shown diagrammatically in FIGURE 1.

In FIGURE 1 metal strip A is shown passing through the finishing stands of a hot mill with its tail end just about to pass through mill stand 0. A second metal strip B is shown closely following strip A so that the head end has just passed through mill stand 7. It is necessary in this instance that looper 3 be down to prevent the head end of strip B from colliding with looper 3. It is also necessary that looper 3 not be cont-rolling the speed of mill stand 7 as it normally would. Sin-ce the strip is passing through the mill train at a considerable speed by the time it reaches or passes looper 2, it is desirable that the raising and lowering of the loopers, starting with looper 2, be initiated before the strip passes out of the controlled stand, or stand 6 in the case of looper 2.

This action is illustrated by loo er 4 which is shown lowering so that it will `be down by the time the tail end of the strip passes out of mill stand 8. It is necessary, however, that the speed of mill stand 8 not be controlled by the movement of the looper as it is lowering away from the strip, and it is also desirable that the speed of the stand not be set to an arbitrary speed While the strip is still in mill stand 8. The present invention, therefore, holds the speed of mill stand 8 at the last controlled speed while the looper 4 is going down and strip A is still in mill stand 3. It is also desirable that the looper not begin lowering as soon as the end of strip leaves the second preceding mill stand, but rather only a predetermined time prior to the exit of the strip from the immediately preceding stand. For instance, looper 3 in FIG-URE 1 did not begin lowering until the tail end of strip A reached approximately the area of dotted line C, and looper 4 did not begin lowering until the tail end of strip A reached approximately the area of dotted line D from which relationship it may be seen that ylooper 4, as shown in FIGURE l, has just begun to lower.

Switch R96 will be closed to activate speed regulator 94 and apply an exciting current to motor field 100 to operate mill stand motor 104. The basic speed of the motor may be controlled or set manually Iby speed adjustment 106. The speed of motor 104 may then be further controlled, faster or slower than the basic speed, by the -use of the speed matching controller, as will now be described.

lin order to prepare the looper control system for automatic operation, switches R215 and R315, shown on FIGURE 3, are closed. If pure manual operation were desired, switch R217 would be manually closed. The closing of switch R215 energizes solenoid 219 which closes automatic control switch 13221. The closure of switch L221 energizes the input of NOR 235 causing NOR 235 to apply a zero signal to input A of NOR 237, which, if it also receives a zero signal at input B from NOR 241 as a result of the input of this NOR being energized by a signal from a substantially similar looper logic circuit associated with looper 2, will put out an energization signal which will be distributed via tap 243 to N-ORs 245 and 2li-7, both of which will then put out a zero signal to place three other NOR elements in what may be described as a go condition at one input such that, if a zero signal is received at their other inputs from other sources, an energization signal will ybe developed from their outputs. NOR 245 activates, or places in a go condition, NORs 251, 277, and 319, while NOR 247 places NORs 283, 309, and 331 in a go condition. Because of the power requirements, it is often impractical for one NOR to activate too large a number of other NOR elements. Since NOR 247 will also receive an energizing signal from manual control switch L225, it will also activate NORs 283, 309, and 331 if manual switch L225 is closed. NOR 237 also sends an energizing signal to the looper logic circuit for looper 4 through terminal 249 indicating that the looper logic circuit for looper 3 has been placed on automatic.

When switch R315 is closed, an energizing signal is applied to the input of NOR 317, causing a zero output .from this NOR to be applied to the inputs of NORs 319, 309 and 331. NORS 309 and 331 are thus placed in a second or double go condition with zero signals to two of their three inputs, the first go condition having been applied by NOR 247 as a result of the system being placed in automatic operating condition. NOR 319, which has only two inputs, both of which are connected to switch controlled activating systems, when it is placed in a double go condition by NORs 317 and 265, immediately ptits out an energizing signal which is amplified by amplifier 321 and applied to the coils of solenoid 323 to close double switch L141, shown in FIGURE 2, and activate the amplit'ier coil 139 of the magnetic ampliiier 97 of controller amplifier 93, placing coil 139 in circuit wtih power transformer 143. This prepares the magnetic amplifier for control action.

With all the appropriate NORs in a go condition and no strip in the mill, memory circuit 271 will be placed in a receptive condition with an energizing signal on the B input of NOR 273 derived through the agency of NORS 279, 277 and 275 from the fact that there is no signal at terminal 281 from the load cell on mill stand 6. At the same time an energizing signal is also placed on the C input of NOR 269 of memory circuit 271 derived through NORs 253, 251 and 263 from the lack of a signal at terminal 255 from the load cell on mill stand 7. Since there is an energizing signal on the receiving inputs B and C of NORs 273 and 269 respectively of memory circuit 271, both these NORs must have zero outputs and the zero output from each NOR is applied to the feedback input A of the other NOR. The zero output of NOR 273 is also applied to the input of NOR 301, which, consequently, puts out an energizing signal, which, after a preset interval, is passed through timing element 303 and applied through tap 304 to the input of NOR 283.

When a strip enters mill stand 6 the load cell of this stand sends a signal to terminal 281, which, as a result of the action of intervening NORs 279, 277, and 275, causes the energizing signal on input B of NOR element 273 of memory circuit 271 to change to a zero signal. Since both inputs of NOR 273 now have zero signals applied to them, NOR 273 puts out an energizing signal which is applied to feedback input A of NOR 269, so that NOR 269 now has two energizing signals, and also applies this energizing signal to the input of NOR 301, which immediately puts out a zero signal which is applied through tap 304 to input A of NOR 283. This places NOR 233 in a double go condition as there is already a zero input to input C of NOR 283 as a result of the system being in automatic operative condition. An energizing signal is still being received at input B of NOR 203, however, from NOR 253 through tap 252.

When the load cell 8A on mill stand 8 applies a signal indicating that a strip is in the bite of the rolls to terminal 255, NOR 253 puts out a zero signal which changes input B of NOR 283 from an energizing signal to a zero signal so that NOR 283 now has an all zero input and in consequence changes its output to an energizing signal which is applied, via tap 285, to amplifier y287 and then to solenoid 289 to operate a valve in the air line to a suitable pneumatic cylinder system to raise looper 3. The energizing signal is also applied to the single input of NOIR 299, which in consequence, puts out a zero signal to input A of NOR 293 which, since its input B is also zero, puts out an energizing signal to amplifier 295 to operate soienoid 297 to open a booster valve in the pneumatic system to accelerate the raising of looper 3. The energizing signal from NOR 283 is also applied, via tap 285, to timing element 291 which holds back the signal for a preset time interval .selected as a desirable period for the boos-ter to remain open. When timing element 291 passes the energizing signal it is applied to input B of NOR 293, causing the output of NOR 293 to go to zero to remove the current from solenoid 297 and allow the booster valve to close and decrease the speed of raising of looper 3.

Meanwhile, the zero output of NOR 253 has also been applied, via tap 252, to input B of NOR 251, the input A of which is already zero as a result of the system being on automatic. NOR 251 puts out an energizing signal which is delayed for a predetermined period by timing element 261 and then applied to the input of NOR 263 which then applies a zero signal to input C of NOR 269. Since NOR 269 is still receiving an energizing signal at its feedback input A from NOR 273, the outputs yof NORs 269 and 273, and, consequently, also the output of memory circuit 271 as a whole, are not changed.

When the strip drops out of mill stand i6, a signal is no longer received at terminal 281 from load cell 6A and this lack of signal is transposed through NO'Rs 279, 277, and 275 to an energizing signal at input B of NOR 273. Since one input of NOR 273 is now energized, it changes its output to zero and applies this zero signal to the feedback input A of NOR 269 and the single input of NOR 301. NOR 301, in consequence, puts out an energizing signal which is delayed for a predetermined period by timer 303 and then applied, via tap 304, to input A of NOR 283, which, in consequence, puts out a zero signal, deenergizing solenoid 289 to allow the air valve in the looper pneumatic system to close and the looper to lower. The delay in Athe energizing signal to input A of NOR 2183 occasioned by timing element 303 is set to provide a sufficient interval for the tail end of the strip to pass from stand 6 to dotted line C in FIGURE 1, and thus allows looper 3 to remain up in controlling position for a longer period. The looper will go from the raised position to the lowered position in the time lit takes the tail end of the strip to pass from the dotted line C to the bite of the rolls in mill stand 7.

After the strip drops out of stand 6 there are two major things which may occur so far as memory circuit 271 is concerned. The rsft would be for the tail end of the strip to next drop out of mill stand 8. This would cause a cessation of the signal a-t terminal 255 from load cell 8A of stand 8 resulting in an energizing signal being applied to input C of NOR 269 through the serial action of NORs 253, 251, and 263. This would alter the `output of 13 NOR 269 to a zero signal which would be applied to the feedback input A of NOR 273 placing all elements of memory circuit 271 in the same condition in which they were originally before any strip entered the mill. The

output of NOR 301 is not altered so that the looper raise p valves remain closed. When a strip entered stand 6 the action just described would merely repeat.

The second major action which may occur is for the head end of a second closely following strip to enter mill stand 6 before the tail end of the irst strip leaves mill stand 8. This might be supposed to place the system in the same condition as when a single strip is in both stands 6 and 8 so that the looper would raise. This, however, is prevented yby memory circuit 27.1, the action of which will now be described.

If a strip enters stand 6 before the preceding strip leaves stand 8, the load cell 6A on stand 6 applies a signal to terminal 281 which, by the serial actions of -NORs 279, 277, and 275, results in the application of a zero signal to input B of NOR 273. This, however, does not alter the output from NOR 273 of memory circuit 271 to NOR 301 since NOR 269 is still sending an energization signal to the feedback input A of NOR 273. The output of NOR '1, therefore, remains the same, and the looper remains down. When the tail end of the first strip leaves stand 8, however, terminal 255 loses its signal from load cell 8A of mill stand 8 and, in consequence, an energization signal is applied to input C of NOR 269 through the serial action of NORs 2513, 251 and 263. This provides a zero output from NOR 269 which is applied to feedback input A of NOR 273. NOR 273 now has a zero signal to both inputs A and B, however, so that the output -of NOR 273 changes to apply an energization signal to feedback input A of NOR 269, and also to the input of NOR 301, which promptly puts out a zero signal, which is applied, via tap 304, to input A of NOR 233. This zero signal to input A might, at iirst thought, be expected to c-ause the loopers to raise. However, when the strip drops out 4of stand 8, load cell 8A no longer supplies a signal to terminal 255, and NOR 253, in consequence, applies an energization signal, via tap 252, to input B of NOR 283 blocking any possible looper raise sign-al. So far as the condition of memory circuit 301 is concerned, however, the system is released for looper raising.

When the load cell 8A on stand 8 next detects a strip in the mill, a zero signal is applied through the intermediate NORs :to input C of NOR 269 in the same manner as if the mill were starting out fresh, and the sequence from then on follows one of the two patterns described above. It will be seen from the foregoing description 'that the looper is successfully prevented from raising between two closely following strips'by the interlock action provided by the memory circuit 271.

While the looper is down or coming up the speed matching control system is maintained by the controller in manual operating condition `by switch L71, shown in FIGURE 2, being close-d. Switch L71 is operated by solenoid 343, shown in FIGURE 3. With switch L71 closed, relays K1 and `K2 are Iactivated and switches K21, K22, and K23 will be open to isolate synchronous converter 51 from the looper bridge circuit. Looper contact arm `13 may still follow the movement of the looper arm, but no potential will be applied to synchronous converter 51, and no control function is thus served by the movements. Switch K12 is also open to remove the output of demodulator 85 from control winding 95 of the magnetic amplier -97 in controller ampliiier 93. At the same time switch K14 is closed to place dummy load 123 in circuit with the output of demodulator 85 in place of the magnetic amplifier coils of the motor control, and switch K13 is colsed to place coils 95 of magnetic amplilier 97 of controller amplifier 93 in circuit with D C. voltage source 117 through potentiometer 119.

If the output of demodulator and potentiometer 119 are not exactly equal and opposite a small current will pass through line and also between taps 125 and 133, in one direction or the other, through resistor-s 131 and 129. Since tap is on the opposite side of resistor 131 from tap 133, there will be a different potential at tap 133 than at tap 135 so long as this small current is owing. It will be readily recognized that, if the output currents of demodulator 85 and potentiometer 119 are equal and opposite, a balance may tbe reached at `which the potentials at tap 135 and tap 133 are exactly equal. Tap 135 during manual operation is connected to tap 137 and contact 61 of synchronous converter 51 by the closing of switch R24. Tap 133 will be connected through cornmon 55 to contact 53 of synchronous converter 51 by the closing of switch K11. Therefore, if the potentials at taps 133 and 135 are not the same, diierent potentials will be placed on the two contacts of synchronous converter 51, and demodulator 85 will direct a control current through dummy load 123 which will increase or decrease until the potentials at taps 135 and 133 are equal. The output of demodulator 85 will thus follow the output of manual control potentiometer 119 to facilitate a so-called bumpless transfer or smooth transition from manual to automatic speed matching control.

A potential is taken of potentiometer 105 and applied to one side of capacitor 109. The potential on the other side of capac-itor 109 is supplied by the bridge circuit 15 through switch K25 so that the potential on contacts 5.3 and 61 will be substantially equal when the controller 1s switched back to automatic control by closing switches K21 and K23, and a possible surge of current or bump in the signal from demodulator 85 is thus avoided.

With automatic control switch L221 in FIGURE 3 closed, the various NORs in go condition, and no strip in any of the mill stands, NOR 339 of mem-cry circuit 337 will have a zero signal to its C input derived from the zero output of NOR 273 of memory circuit 271 as a direct result of no strip detection signal being received from load cell 6A. NOR 335 of memory circuit 337 will receive an energizing signa-l at yinput B derived from NOR 263 through input C of OR 329, input A of NOR 331, and NOR 333 as a result of no strip being detected by load cell 8A; and NOR 327, input A of OR 329, input A of NOR 31, and NOR 333 as a result of no strip being detected by the load cell 7A. Since an energization signal is received at input B of NOR 335, this NOR has a zero output which is applied to feedback input A of NOR 339 and also amplifier 341.

Since allthe inputs of NOR 339 of memory circuit 337 are therefore receiving zero signals, the output of NOR 339, which is applied to the feedback input A of NOR 335, is an energization signal.

When a strip enters stand 6 an energization signal Will appear at input C of NOR 339 and a zero signal will then be applied to the feedback input A of NOR 335 by the output of NOR 339. When a strip enters mill stand 7 the energization signal at input B of NOR 335 due to NOR 327 will theoretically turn to zero but will in reality remain energized due to the signal being received from NOR 263. When strip enters stand 8 a signal from load cell 8A will be detected by NOR 253, which will app-ly a zero signal to input B of NOR 251, which will, in turn, apply an energization signal to timing element 261, which will delay the signal for a suitable predetermined period suiiicient for the looper to raiseit will lbe recalled that at this point memory circuit 271 has already released the looper for raising and the looper raise pneumatic valves are opened as soon as NOR 253 applies a zero signal, via tap 252, to input B of NOR 28E-and then will apply the energization signal to NOR 263 which in consequence provides a zero signal to input: C of OR 329 via tap 345, input A of NOR 331, and .an energization signal to NOR 333 which provides a zero signal to input B of NOR 335 of memory circuit 337. Since NOR 335 already has a zero signal at its feedback input A, it will now put out an energization signal which is applied to feedback input A of NOR 339 and also to amplifier 341 which provides an energization current to solenoid 343 to open switch L71, shown in FIGURE 2, and deactivate relays K1 and K2 to close switches K21, K22, R23, and K12 and open switches K11, K13, K14, K24, and K25 to activate the automatic speed matching control system. The delay caused by timer 261 prevents automatic control of the speed of rolls instand 7 from being taken over by the looper control system until the looper has come up and contacted the strip.

Since switch L31, which allows current to pass through the looper bridge circuit, is normally closed, if the looper contact arm 13 and setpoint arm 21 are not balanced, a current will ow between the contact arms. The potential at tap 43 between resistors 23 and 25 will be applied to contact 53 of converter 51. A second potential will be applied to contact 61 of converter 51 from capacitor 109. If these potentials are not equal, an alternating potential will be imposed on capacitor 81, amplied in amplier 83, and demodulated and used to control a DC. power circuit source in demodulator 85. Demodulator 85 will provide a current through coils 95 of magnetic amp-lier 97 in the controller amplifier 93, the output of which changes the degree of saturation on the magnetic amplifier, not shown, in the speed regulator 94;, which controls the mill motor 104 in stand 7. As the speed of the motor 104 is varied to alter the amount of slack in the strip between the mills, the position of the looper arm is correspondingly varied. The looper contact arm 13 is thereby moved in an appropriate direction to balance the bridge circuit and remove the potential difference from the contacts of converter 51. Because of the resistors 65 and 63 the potential on contact 61 will in the long run be zero with respect to vibrating contact 79. As a result, the potential on contact 53 will also over a period approach or reach zero. In order for the potential on contact 53 to be zero, the current in resistor 25 must also be zero. This will only occur when the position of looper contact arm 13 on resistance 17 corresponds resistively to the position of contact arm 21 on the set point resistance 19.

Feedback potential through capacitor 109 from the lload circuit tends to oppose the effect of a change in the error signal from bridge circuit 15. If the load condition is changing, this feedback decreases the possibility of overcorrection. At the same time a rate adjustment potential is obtained from tap 113 and applied to capacitor 115 to modify the potential applied to contact 53 if the error signal put out by bridge circuit is changing rapidly.

As demodulator 85 applies more current to the speed regulator circuit, a greater amount of current passes through potentiometer 105 and resistor 107. A potential is tapped oiic potentiometer 105 and applied through capacitor 109 to contact 61 of converter 51. The current applied to the speed regulator circuit by demodulator 85 is controlled by the potential difference between contacts 53 and 61. A different potential at contact 53 results in a greater current through the speed regulator circuit. The increase in the output of demodulator 85 is fed back by a greater potential across potentiometer 105 tapped off and applied through capacitor 109 to contact 61. With suicient increase in speed regulator current, therefore, the potential `difference between contacts 53 and 61 will disappear, stabilizing the output of dernodulator 85. Because of the presence of reset variable resistor 65, capacitor 109 is charged, however, over a time period dependent upon the setting of variable resistor 65, to a voltage equal to and opposing the potential existing between the arm of potentiometer 105 and common 55 and the potential difference rbetween con tact 61 and common 55 therefore tends always to approach zero, If', as this ypotential approaches zero, a dif- CII ference in potential between contacts 53 and 61 of converter 51 reappears, because the output of bridge 15 is not yet zero, the current in the speed regulator circuit will be changed again. This cycle will continue until the error signal from bridge circuit 15 finally disappears. The speed of the mill motors on stand 7 are thus controlled to keep the correct `looper position needed to maintain the error signal from bridge circuit 15 at zero.

As long as memory circuit 271, in FIGURE 3, calls for the looper to be lowered, NOR 305 will provide a zero signal to input A of NOR 307. Also as long as strip is in stand 8 NOR 263 will supply a zero signal to input B of NOR 307. The two zero inputs to NOR 307 cause it to apply an energizing signal to input A of NOR 309 and solenoid 320, consequently, is not energized so that switch L31 is open to prevent an error signal from being given out by the looper control bridge circuit 15. When a looper raise signal is provided by memory circuit 271, a zero signal is applied to the input yof NOR 305, which then applies an energization signal to input A of NOR 307, resulting in a zero signal to input A of NOR 309 which, since its inputs B and C also have zero signals to place it in an intial go condition, gives out an energization signal to ,amplifier 318, which in turn energizes solenoid 320 to close switch L31, in FIGURE 2, and energize the looper control bridge circuit.

When the strip drops out of stand 6 an energization signal is given out by NOR 301 through timer 303 which delays the signal for a period sufficient for the strip to reach dotted line C in FIGURE 1, or, in other words, until looper 3 begins to lower, and then passes `the energization signal on to the input of NOR 305, which then against provides a zero signal to input A `of NOR 307 to provide an energization signal to input A of NOR 309, which then develops a zero output deenergizing solenoid 320 and allowing switch L31 to open while the looper is going down. Since relays K1 and K2 stay on automatic even though the looper energization current is removed, the controller maintains the last controlled speed of stand 7 until the system is placed on manual control when the strip drops out of stand 7, as will next be de.- scribed.

As previously described, while strip is in stands 6, 7, and 8 memory circuit 337 will give out an energization signal to amplifier 341 to open switch L71 in FIGURE 2. NOR 335 will have a zero signal applied to its B input as a result of strip being in stands 7 and 8, and a zero signal applied to its A feedback input from NOR 339 which is receiving two energization inputs. When the strip drops out of stand 6 the signal from NOR 273 of memory element 271 changes from an energization signal to a zero signal which is applied to input C of NOR 339. NOR 335, however, s'till continues to receive a zero feedback signal at input A from NOR 339 because NOR 339 is likewise still receiving an energization feedback signal at input A from NOR 335, which also continues to apply an energization signal to solenoid 343 through amplifier 341 to maintain switch L71 open. Automatic control thus continues even though, as described hereinabove, a zero signal is derived from NOR 305 after a suitable interval, determined by timer 303 to allow the strip to reach dotted line C in FIGURE l, which zero signal ultimately results in the deenergization of solenoid 320 to open switch L31 and thus remove the error signal normally received from the looper bridge circuit 15.

After the strip drops out of stand 6 there are two sequences which may be followed. If a second strip is picked up by stand 6 before the tail end of the first strip drops out of stand 7, the signal from NOR 335 remains the same because the signal from NOR 273 remains zero due to a feedback energization signal at input A, even though the signal to input B changes to zero. NOR 335, therefore, continues to energize solenoid 343 and automatic speed control continues. When the strip now drops out of stand 7, NOR 327 gives an energization output signal which ultimately removes the zero signal from input B of NOR 335. When input B receives an energization signal, a zero feedback signal is applied to input A of NOR 339, which is already receiving a zero signal from memory element 271-which is not altered in any way by the strip dropping out of stand 7 since memory .element 271 is connected only to stands 6 and 3-and in consequence an energization feedback signal is applied to input A of NOR 335. NOR 335 puts out a Zero signal deenergizing solenoid 343, and allowing switch L71 to close and pla-ce the system on manual speed control, which will have had a suitable manual speed preset upon it. When the strip drops out of stand 8, the signal from memory circuit 271 changes to an energization signal which is applied to input C of NOR 339 while input B of NOR 335 remains energized since no signal is received from stand 7. NOR 335 continues to put out a zero signal, therefore, and solenoid 343 remains deenergized. Even if a following strip enters stand 7 just as the first strip leaves stand 8, input B of NOR 335 remains energized, and NOR 335 must, therefore, continue to put out a zero signal. Supposing, however, that the two strips are following very close together, if the following strip should enter stand 7 before the first strip leaves stand 8, a zero signal would be applied to input B of NOR 335 `derived from the load cells of both stands 7 and 8. A zero signal is still maintained on input C of NOR 339, however, because NOR 273 of memory circuit 271 continues to provide a zero signal until strip drops out of stand 8. Feedback input A of NOR 339 is also receiving a zero signal from NOR 335, because NOR 335 continues to receive an energization feedback signal at input A from NOR 339, and NOR 335, therefore, also continues to sup-ply a zero signal to amplifier 341, and solenoid 343 remains deenergized to maintain the system on manual control. It will be seen that the only way to remove the zero output signal from the memory circuit 337 is -for the strip to drop out of stand 8 to remove the zero signal from input C of NOR 339. Once this occurs, then, when strip reenters stand 8, the operation sequence will be repeated and the automatic speed control will be reinstituted-with a suitable interval effected by timer 261 to allow the looper to raise. It will thus be seen that automatic speed control of the system, once it has been interrupted, like raising of the looper once it has been lowered, .cannot be effected, because of the logic interlock elements of the system, until the signal from the load cell 8A has been interrupted and then reinstituted, indicating that a strip has dropped out of stand 8 and a second strip has been picked up.

In FIGURE 3 it will be seen that closing of switch L225 to initiate complete manual operation will, through appropriate connections, either bypass or activate all elements of the logic control system except the solenoids 323 which activates switch 141 in FIGURE 2 to activate amplifier coils 139, and solenoid 343, which opens switch L71 to deenergize solenoids K1 and K2 to activate automatic speed control. It will be noted, for instance, that a signal from manual switch L225 may be applied to input B of OR 259 in place of the normal signal from the load cell of stand S at input A of OR 259. Signals from switch L225 are conducted to appropriate NORs to substitute for the input signals of stands 6 and 7 also and therefore by closing switch L225 by manual switch 217 to operate solenoid 223 the loopers may be raised manually to take up slack at any time. Part of the logic circuit is also operated for convenience in checking circuits when switch L225 is closed, as though strip were in all three stands in the correct sequence, whether strip is actually present or not. If switch R315 is not closed when on automatic, the looper may be raised with automatic sequencing without activating the speed matching system, and the loopers may be used merely to take up the slack between the mill stands, leaving the mill operator to adjust the speeds of the mill stands individually by conventional manual controls at each mill stand. If the system is placed on pure manual by the operation of switch R217 to energize solenoid 223 and close manual switch L225, switch L141, shown in FIGURE 2, will be open, deenergizing magnetic amplifier 97, and motor 104 may be operated through speed regulator 94, if power switch R96 is closed, and the speed of the motor 104 may then be manually controlled by means of speed adjustment 106.

All the loopers are similar in operation and are controlled by substantially identical control systems, as described hereinbefore, with the exception of looper 5E which, as has been mentioned, is connected to control the speed of succeeding stand 10 rather than stand 9, which is the pivot stand, and looper 1, the control system of which is responsive to signals from the load cell of preceding stand 5, rather than a second preceding stand as in the other loopers, for the initiation of the lowering cycle and which does not include a speed holding cycle since the looper does not begin to lower until the strip leaves stand 5, the speed of which looper 1 controls. Since the strip is not moving at as high a rate of speed in the initial stands as in the later stands, looper 1`has sufiicient time to lower before the tail end of the strip reaches the looper.

I claim:

1. In a multi-stand rolling mill adapted to operate simultaneously on a work piece and having at least one looper positioned between two successive stands and adapted to control the speed of the next preceding stand, a control system for the looper comprising:

(a) means associated with a preceding stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) means associated with the next succeeding stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand, and

(c) means for raisin-g the looper in response to, and

only to, the following signals from said signal generating means, viz.

(i) a signal from a preceding stand indicating the presence of strip therein,

(ii) a signal from the next succeeding stand indicating the absence of strip therein, and

(iii) a subsequent signal from said next succeeding stand indicating the presence of strip therein.

2. In a strip rolling mill comprising a first roll stand, a second roll stand, a third roll stand, and a looper positioned between Ithe second roll Stand and the third roll stand and adapted to control the speed of the second stand, the improved means for controlling the position of the looper comprising:

(a) electrical signal means associated with the rst roll stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand, p

(b) electrical signal means associated with the third roll stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in vthe stand, and

(c) static logic circuit means for raising the looper in response to, and only to, the following signals from said signal generating means, viz.

(i) a signal from the first stand indicating the presence of strip therein,

(ii) a signal from the third stand indicating the absence of strip therein, and

(iii) a subsequent signal from said third stand indicating t-he presence of strip therein.

3. In a strip rolling mill comprising a first roll stand, a

second roll stand, a third roll stand, and a looper posi- 19 tioned between the second'roll s-tand and the third roll stand and hav-ing means responsive to the position of the looper for regulating the speed of the second roll stand, the improve-d control means for the looper comprising:

(a) separate means associated with each mill stand for generating a first signal indicative of the presence of strip in the stand and a second signal indic-ative of the absence of strip in the stand,

(b) means responsive to signals indicating the presence of strip in the first and third roll stands to raise the looper into position against the strip,

(c) means responsive to the position of said looper against the strip to control the speed of the second st-and,

(d) means responsive to a signal from the signal generating means associated with the first mill stand which signal is indicative of the absence of strip in said stand for lowering the looper out of contact with the strip and for maintaining the speed of the second stand at a predetermined value.

4. In a strip rolling millcomprising a first roll stand,

a second roll stand, a third roll stand, and a looper positioned between the second roll stand and the third roll stand and having means responsive to the position of the looper for regulating the speed of the second roll stand, the improved control means for the looper comprising:

(a) separate means associated with each mill stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) means responsive to signal indicating the presence of strip in the first and third roll stands to raise the looper into position against the strip,

(c) means responsive to the position of said looper against the strip to control the speed of the second stand,

(d) means responsive to a signal from the signal generating means associated with the first mill stand which signal is indicative of the absence of strip in said stand for lowering the looper out of contact with the strip, and

(e) timing means to delay the action of the looper lowering means a predetermined time.

5. in a strip rolling mill comprising a rst roll stand,

a second roll stand, a third roll stand, and a looper positioned between the second roll stand and the third roll stand and having means responsive to the position of the looper for regulating the speed of the second roll stand, the improved control means for the looper comprising:

(a) separate means associated with each mill stand for generating a first signal indicative of the presence of strip in the stand and Aa second `signal indicative of the absence of strip in the stand,

(b) means responsive to signals indicating the presence -of strip in the first and third roll stand to raise the looper into position against the strip,

(c) means responsive to the position of said looper against the strip to control the speed of the second stand,

(d) means responsive to a signal from the signal generating means associated with thel `first mill stand which signal is indicative of the absence of strip in said stand for lowering the looper out of contact with the strip,

(e) timing means to delay the action of the looper lowering means a predetermined time, and

(f) means to maintain the speed of the second stand `at the last speed controlled by the looper before the looper begins to lower until the strip passes out of the second roll stand.

6. In a strip rolling mill comprising a first roll stand, a second roll stand, a third roll stand, and a looper positioned between the second roll stand and the third roll stand and having means responsive to the position of the looper for regulating the speed of the second roll stand, the improved control means for the looper comprising:l

(a) separate means associated with each mill stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) means responsive to signals indicating the presence of strip in the first and third roll stands to raise the looper into position against the strip,

(c) means responsive to the position of said looper against the strip to control the speed of the second stand,

(d) means responsive to a signal from the signal generating means associated with the first mill stand which signal is indicative of the absence of strip in said stand for lowering the looper out of contact with the strip,

(e) timing means to `delay the action of the looper lowering means a predetermined time,

(f) means to maintain the speed of the second stand a-t the last speed controlled by the looper before the looper begins to lower until the strip passes out of the second roll stand, and

(g) means responsive to the signal from the signal generating mea-ns asociated with the second stand which signal is indicative of the absence of strip in said stand for altering the speed of the stand to a predetermined value.

7. In a strip rolling mill comprising a first roll stand,

a second roll stand, a third roll stand, and a looper positioned between the second roll stand and the third roll stand and adapted to control the speed of the second stand, the improved means for controlling the position of the looper comprising:

(a) means associated with each mill stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) logic circuit means responsive to signals indicating the presence of strip in the first and third mill stands to raise the looper intoiposition against the strip,

(c) electrical signal means responsive to the position of said looper against the strip to control the speed of the second stand,

(d)l logic circuit means responsive to a signal from the signal generating means associated with the first mill stand which signal is indicative of the absence of strip in said stand for lowering the looper out of contact with the strip,

(e) logic circuit means for reraising the looper in response to, and only to, the following signals front said signal generating means, viz.

(i) a signal from the first mill stand indicating the presence of strip therein,

(ii) a signal from the third stand indicating the absence of strip therein, and

(iii) a subsequent signal from the third mill stand indicating the presence of strip therein.

8. In a strip rolling mill comprising a first roll stand,

a second roll stand, a third roll stand, and 4a looper positioned between the second roll stand and the third roll stand and adapted to control the speed of the second stand, the improved means for controlling the position of the looper comprising:

(a) means `associated with each millV stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) logic circuit means responsive to signals indicating the presence of strip in the first and third mill stands to raise the looper into position against the strip,

(c) electrical signal means responsive to the position of said looper against the strip to control the speed of the second stand,

(d) logic circuit means responsive to a signal from the signal generating means associated with the first mill stand which signal is indicative of the absence of strip in said stand for lowering the looper out of contact with the strip Iafter a preset time determined by a timing means,

(e) logic circuit means for holding the speed of the second mill stand at the last speed controlled by the looper after the preset time determined by the timing means,

(f) logic circuit means responsive to a signal from the signal generating means associated with the second mill stand which signal is indicative of the absence of strip in said stand for setting the speed of the mill to a predetermined speed,

(g) first logic memory circuit means for reraising the looper in response to, and only to, the following signals from said signal generating means, Viz.

(i) a -signal from the first mill stand indicating the presence of strip therein,

(ii) a signal from the third stand indicating the absence of strip therein,

(iii) a subsequent signal from the third mill Stand indicating the presence of strip therein,

(h) a second logic memory circuit means effecting control of the speed of the second mill stand by the movements of the looper, in response to, and only to, the following signals from said signal generating means, viz.

(i) a signal from the first mill stand indicating the presence of strip` therein, (ii) a signal from the third mill stand indicating the absence of strip therein, (iii) a subsequent signal from the third mill stand indicating the presence of strip therein, and (iv) a continuing signal from the second mill stand indicating the presence of strip therein.

9. In a multi-stand rolling mill adapted to operate simultaneously on a work piece and having at least one looper positioned between two successive stands and adapted to control the speed of the next preceding stand, a control system for the looper comprising (a) means associated with a preceding stand for generating a rst signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) means associated with the next succeeding stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand, and

(c) means for raising the looper in response to the following signals from said signal generating means, viz.

(i) a signal from a preceding stand indicating the absence of strip therein,

(ii) a subsequent signal from the preceding stand indicating the presence of strip therein,

(iii) a signal from the next succeeding stand indicating the absence of strip therein, (iv) a subsequent signal from said next succeeding stand indicating the presence of strip therein, (v) the signal from the preceding stand indicating the absence of strip therein occurring prior to the signal from the succeeding stand indicating the absence of strip therein. 10. In a strip rolling mill comprising a iirst `roll stand,

a second roll stand, a third roll stand, and a looper positioned between the second roll stand and the third roll stand and adapted to control the speed of the second stand, the improved means for controlling the position of the looper comprising:

(a) means associated with each mill stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) logic circuit means responsive to signals indicating the presence of strip in the first and third mill stands to raise the looper into position against the strip,

(c) electrical signal means responsive to the position of said looper against the strip to control the speed of the second stand,

(d) logic circuit means responsive to a signal from the signal generating means associated with the iirst mill stand which signal is indicative of the absence of strip in said stand for lowering the looper out of contact with the strip after a preset time determined by a timing means,

(e) logic circuit means for holding the speed of `the second mill stand at the last speed controlled by the looper after the preset time determined by the timing means,

(f)logic circuit means responsive to a signal from the signal generating means associated with the second mill stand which signal is indicative of the absence of strip in said stand for setting the speed of the mill to a predetermined speed,

(g) first logic memory circuit means for reraising the looper in response to the following signals from said signal generating means, viz.

(i) a signal from the first mill stand indicating the absence of strip therein,

(ii) a subsequent signal from the rst mill stand indicating the presence of strip therein,

(iii) a signal from the third mill stand indicating the absence of strip therein,

(iv) a subsequent signal from the third mill stand indicating the presence of strip therein,

(v) the signal from the first stand indicating the absence of strip therein occurring prior to the signal from the third stand indicating the absence of strip therein,

(h) Ia second logic memory circuit means effecting control of the speed of the second stand by the movements lof the looper in response to, and only to, the following signals (i) a signal from the first mill stand indicating the absence of strip therein,

(ii) a subsequent finite signal from the first mill stand indicating the presence of strip therein,

(iii) a signal from the third mill stand indicating the absence of strip therein,

(iv) a subsequent signal from the third mill stand indicating the presence of strip therein,

(v) a continuing signal from the second mill 'stand indicating the presence of strip therein,

and

(vi) the signal from the first mill stand indicating absence of strip therein -occurring prior to the signal from the third mill stand indicating the yabsence of strip therein.

11. In a multi-stand rolling mill adapted to operate simultaneously on a Work piece and having loopers between at least some successive stands and adapted to control the speed of associated stands on the same side of eac-h of the respective loopers, a control system for the loopers comprising:

(a) means responsive to the position of the loopers `against the work piece to control the speed of adjacent stands,

(b) separate `control systems for each looper and associated controlled stand, (c) said control systems having a manual condition in which the speed of the mill stands may be pre determined without reference to the looper position and an automatic condition in which the speed of the mill stands are responsive to the position of said looper against the workpiece during some period of operation,

(d) interlock means associated with each looper control system to prevent it from being placed in said automatic condition until the looper control system of the looper between the stand, the speed of which is controlled by the position of the rst looper, and the next adjacent stand is also placed in said automatic condition.

l2. In a multi-stand rolling mill adapted to operate simultaneously on a work piece comprising:

(a) a series of loopers between succeeding mill stands,

(b) a mill stand having an automatic gauge control for the control of strip gauge associated therewith and constituting a pivot stand for the loopers,

(c) control system means responsive to the position against the work piece of any looper in the mill before the pivot stand to control the speed of the next preceding mill stand,

(d) control system means responsive to the position against the work piece of `any looper in the mill after the pivot stand to control the speed of the next succeeding mill stand,

(e) each said control system means having a manual condition in which the speed of the mill stand may be predetermined without reference to the looper position and an automatic position in which the speed of the mill stand is responsive to the position of said looper against the workpiece during some period of operation, and

(f) interlock means associated with each looper control system to prevent it from being placed in said automatic condition until the looper control system of the looper between the stand, the speed of which is controlled by the position of the looper, and the next adjacent stand lis also placed in said automatic condition.

13. A method of operating a multi-stand rolling mill with stands adapted to -operate simultaneously on a work piece and having at least one looper positioned between two successive stands comprising:

(a) passing strip through the mill,

(b) detecting the presence of strip in the mill stands second preceding, next preceding, and next succeeding a looper with signaling means,

(c) raising the looper as strip enters the three adjacent mill stands only after strip has been simultaneously detected by the signaling means in the second preceding mill stand and the next succeeding mill stand,

(d) controlling the speed of the next preceding mill stand according to changes in signals derived from the position of the looper against the Work piece,

(e) lowering the looper a predetermined time after strip ceases to be detected by the signaling means in the second preceding stand,

(f) discontinuing control of the speed of the next preceding mill stand according to changes in signals derived from the position of the looper against the work piece a predetermined time after strip ceases to be detected by the signaling means in the second preceding stand,

(g) maintaining the speed of the next preceding mill stand at the last speed controlled according to said movements of the looper against the work piece between the predetermined time after strip ceases to be detected by the signaling means in the second preceding mill stand and a time when strip ceases to be detected in the next preceding stand, and

(h) resetting the speed of the next preceding stand to a predetermined value when strip ceases to be detected in the next preceding stand.

14. A method of operating a multi-stand rolling mill With stands adapted to operate simultaneously on a work piece and having at least one looper positioned between two successive stands comprising:

(a) passing strip through the mill,

(b) detecting the presence of strip in the mill stands second preceding, next preceding, and next succeeding a looper with signaling means,

(c) raising the looper as strip enters the three adjacent mill stands only after strip has been simultaneously detected by the signaling means in the second preceding mill stand and the next succeeding mill stand,

(d) controlling the speed of the next preceding mill stand according to changes in signals derived from the position of the looper against the work piece,

(e) lowering the looper a predetermined time after strip ceases to be detected by the signaling means in the second preceding stand,

(f) discontinuing control of the speed of the next preceding mill stand according to changes in the signals derived from the position of the looper against the work piece a predetermined time after strip ceases to be detected by the signaling means in the second preceding stand,

(g) maintaining the speed of the next preceding mill stand at the last speed controlled according to said movements of the looper against the work piece between the predetermined time after strip ceases to be detected by the signaling means in the second preceding mill stand and a time when strip ceases to be detected in the next preceding stand,

(h) resetting the speed of the next preceding stand to a predetermined value when strip ceases to be detected in the next preceding stand,

(i) maintaining the looper in lowered position and the speed of the mill at said predetermined value at least until the strip ceases to be detected in the next succeeding mill stand,

(j) when strip is again detected simultaneously in the second preceding and succeeding mill stands raising the looper, and

(k) controlling the speed of the next preceding mill according to the position of the looper against the strip a predetermined time after strip is again simultaneously detected in the second preceding and next succeeding mill stands.

15. In a multi-stand rolling mill having stands adapted to operate simultaneously on a work piece and having at least two loopers separated by an adjacent stand to control the speed of separate adjacent stands, a control arrangement for the loopers comprising:

(a) means associated with the second preceding, next preceding and next succeeding mill stand with respect to each looper for generating a first signal indicative of lthe presence of strip in each of the respective stands and a second signal indicative of the absence of strip in each of the respective stands,

(b) means responsive to the position of each respective looper against the work piece to contr-ol the speed of an adjacent stand, which stand is next adjacent the stand controlled by the next adjacent looper,

(c) a control system for each looper for the separate control of each looper,

(d) said control systems having a manual condition in Which the speed of the associated stands may be predetermined without reference to the looper position and an automatic condition in which the speed of the associated stands are responsive to the position of said looper against the work piece during some period of operation,

(e) means associated with each looper control system to prevent it from being placed in said automatic condition until the looper control system of the looper lbetween the stand, the speed of which is controlled by the position of the rst looper, and the next adjacent stand is also placed in said automatic condition,

(f) means for raising each respective looper in response to, and only to, the following signals from said signal generating means, viz.

(i) a signal from a preceding stand indicating the the presence of strip therein,

(ii) a signal from the next succeeding stand indicating the absence of strip therein,

(iii) a subsequent signal from said next succeeding stand indicating the presence of strip therein,

(g) means for initiating control of the speed of the mill stand preceding the respective looper in response to, and only to, the following signals from said signal generating means, viz.

(i) a signal from a preceding mill stand indicating the presence of strip therein,

(ii) a signal from the next succeeding stand indicating the absence of strip therein,

(iii) a subsequent signal from the next succeeding mill stand indicating the presence of strip therein,

(iv) a continuing signal from the next preceding mill stand indicating the presence of strip therein,

(h) timing means to delay the initiation of control of the speed of the next preceding stand in response to -said signals,

(i) means for lowering at least one respective looper in response to a signal from the signal generating means associated with the second preceding stand indicative of the absence of strip in the stand,

(j) timing means for delaying a predetermined time the l-owering of the respective looper in response to a signal from the signal generating means associated with the second preceding stand indicative of the absence of strip in the stand,

(k) means to maintain the speed of the next preceding stand at the last speed controlled in response to the movements of the respective looper before the looper lowers until a signal is received from the generating means associated with the next preceding stand indicative of the absence of strip in said stand,

(l) means to adjust the speed of the next preceding mill stand to a predetermined speed when the generating means associated with the mill stand next preceding the respective looper generates a signal indicative of the absence of strip in the stand.

16. In a strip rolling mill comprising at least a lirst roll stand, a second roll stand, a third roll stand, and a looper positioned between the second `roll stand and the third roll stand and adapted to control the speed of the second stand through automatic control means, the improved means for controlling the position of the looper comprising:

(a) load cell means associated with each mill stand for generating a rst signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) static logic circuit means responsive to signals from the load cell means indicating the presence of strip in the tirst and third mill stands to raise the looper into position against the strip,

(c) static logic circuit means responsive to a signal from the load cell means associated with the first mill stand, which signal is indicative of the absence ot strip in said stand, for lowering the looper out of contact with the strip,

(d) static logic memory element circuit means for reraising the looper in response to, and only to, the following signals from said load cell signal generating means, viz.

(i) a signal from the load cell means associated with the rst mill stand indicating the presence of strip therein,

(ii) a signal from the load cell means associated with the third mill stand indicating the absence of strip therein, and

26 (iii) a subsequent signal from the load cell associated with the third mill stand indicating the presence of strip therein. 17. In a strip rolling Imill comprising a lirst roll stand,

a second roll stand, a third roll stand, and a looper positioned between the second roll stand and the third roll stand and adapted to control the speed of the second stand, the improvedmeans for controlling the position of the looper and the speed o'f the mill comprising:

(a) load cell means mounted upon each mill stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative ofthe absence of strip in the stand,

(b) static logic circuit means responsive to signals indicating the presence of strip in the first and third mill stands to raise the looper into position against the strip,

(c) an automatic controller responsive to the position of said looper against the strip through electrical circuit detecting means, and the speed of the mill motor through electrical feedback meansl to control the speed of the second stand,

(d) static logic circuit means responsive to a signal from the load cell means associated with the first mill stand which signal is indicative of the absence of strip in said stand for lowering the looper out of contact with the strip after a preset time determined by a timing means,

(e) static logic circuit means for -controlling the automatic controller means for holding the speed of the second mill stand at the last speed controlled by the looper through the automatic controller means after the preset time determined Iby the timing means,

(f) static logic circuit means responsive to a signal from the load cell means associated with the second mill stand which signal is indicative of the absence of strip in said stand for setting the speed of the mill to a predetermined speed set on the: automatic control means,

(g) first static logic memory circuit means for reraising the looper in response to, and only to, the following signals from said load cell means, viz.

(i) a signal from the load cell on the rst mill stand indicating the presence of strip therein,

(ii) a signal from the load cell means on the third mill stand indicating the absence of strip therein,

(iii) a subsequent signal from the load cell means on the third mill stand indicating the presence of strip therein,

(h) a second static logic memory circuit means for effecting control of the speed of the second mill stand through the automatic control means by movements of the looper, in response to, and only to, the following signals from said load cell means, viz.

(i) a signal from the load cell means on the rst mill stand indicating the presence of strip there- 1n,

(ii) a signal from the load cell means on the third mill stand indicating the absence of strip therein,

(iii) a subsequent signal from the load cell means on the third mill stand indicating the presence of strip therein, and

(iv) a continuing signal from the load cell 4means on the second mill stand indicating the presence of strip therein.

18. In a multi-stand rolling mill with adjacent stands adapted to operate simultaneously on a workpiece and having at least one looper positioned `between successive stands and adapted to control the speed of the next preceding stand, the improved fmeans for controlling the position of the looper comprising:

(a) electrical signal means associated with a preceding stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand,

(b) electrical signal means associated with the next succeeding stand for generating a lirst signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand, and

(c) static logic circuit means for raising the looper in response to, and only to, the following signals from said electrical signal generating means, viz.

(i) a signal from said preceding stand indicating the presence of strip therein,

(ii) a signal from the next succeeding stand indicating the absence of strip therein, and

(iii) a subsequent signal from said next succeeding stand indicating the presence of strip therein.

19. In a strip rolling mill comprising a first roll stand and a second roll stand, a control system to control a physical operation of the mill at a location `between a point immediately preceding the first roll stand and a point immediately succeeding the second roll stand cornprising:

CIK

(a) a signal generating means associated with the irst roll stand for generating a rst signal indicative of the presence of strip in said stand and a second signal indicative of the absence of strip in said stand,

(b) signal generating means associated with the second roll stand for generating a first signal indicative of the presence of strip in said stand and a second signal indicative of the absence of strip in said stand, and

(c) logic circuit means for controlling said operation of the mill in response to, and only to, the following signals from said signal generating means, viz.

(i) a signal from the rst stand indicating the presence of strip therein,

(ii) a signal from the second stand indicating the absence of strip therein, and

(iii) a subsequent `signal from said second stand indicating the presence of strip therein.

No lreferences cited.

20 WILLIAM W. DYER, JR., Primm-y Examiner. 

1. IN A MULTI-STAND ROLLING MILL ADAPTED TO OPERATE SIMULTANEOUSLY ON A WORK PIECE AND HAVING AT LEAST ONE LOOPER POSITIONED BETWEEN TWO SUCCESSIVE STANDS AND ADAPTED TO CONTROL THE SPEED OF THE NEXT PRECEDING STAND, A CONTROL SYSTEM FOR THE LOOPER COMPRISING: (A) MEANS ASSOCIATED WITH A PRECEDING STAND FOR GENERATING A FIRST SIGNAL INDICATIVE OF THE PRESENCE OF STRIP IN THE STAND AND A SECOND SIGNAL INDICATIVE OF THE ABSENCE OF STRIP IN THE STAND, (B) MEANS ASSOCIATED WITH THE NEXT SUCCEEDING STAND FOR GENERATING A FIRST SIGNAL INDICATIVE OF THE PRESENCE OF STRIP IN THE STAND AND A SECOND SIGNAL INDICATIVE OF THE ABSENCE OF STRIP IN THE STAND, AND (C) MEANS FOR RAISING THE LOOPER IN RESPONSE TO, AND ONLY TO, THE FOLLOWING SIGNALS FROM SAID SIGNAL GENERATING MEANS, VIZ. (I) A SIGNAL FROM A PRECEDING STAND INDICATING THE PRESENCE OF STRIP THEREIN, (II) A SIGNAL FROM THE NEXT SUCCEEDING STAND INDICATING THE ABSENCE OF STRIP THEREIN, AND (III) A SUBSEQUENT SIGNAL FROM SAID NEXT SUCCEEDING STAND INDICATING THE PRESENCE OF STRIP THEREIN. 